1. Field of the Invention
This invention relates to a photocell utilizing the cell reaction between Ag and a halogen produced by photodissociation of silver halides and particularly AgBr, AgI and the like and showing high conversion efficiency.
2. Description of the Prior Art
It has been long known that silver halides undergo photodissociation and this phenomenon has been utilized in the photographic art and photochromic glasses.
An attempt has been made to fabricate primary cells which include a layer of solid electrolyte of a silver salt such as RbAg.sub.4 I.sub.5 or Ag.sub.3 SI, a positive electrode formed on one side of the solid electrolyte layer and made of a mixture of a halogen (mainly, iodine) and graphite or a charge transfer complex such as PbI.sub.3, NR.sub.4 I.sub.3 (in which R represents an alkyl group), and a negative electrode of Ag formed on the other side. However, the primary cells have not been reduced to practice yet since the materials themselves are expensive and output power per cost is small.
There has been made a further attempt to manufacture cells which have an AgI or AgBr electrolyte layer, a transparent electrode formed on one side of the electrolyte layer, and a graphite electrode formed on the other side, the halogen which has been photodissociated by light passing through the transparent electrode being absorbed by the graphite electrode. However, the cells of this type have disadvantages that the thickness of the electrolyte layer must be below 10 microns to attain a cost per unit power of as low as about 100 yen/W. However, when the electrolyte layer is controlled to have such a small thickness as mentioned above, the cell can only stand repeated use of at most several cycles and absorption of halogen in the graphite electrode is so slow and so small in amount that the quantum efficiency becomes poor.
In recent years, the price of petroleum has risen sharply and efficient use of solar energy as a substitute for petroleum has been extensively investigated. Because of its low energy density on the surface of the earth and its seasonal, timewise and weather related variations, some difficulties are involved in practical use of solar energy. At present, solar energy is merely utilized thermally in most cases. In addition, in satellites or beacons in remote places, solar cells are sometimes used in combination with secondary cells but have the drawback that the power generation cost is as high as 2,000 to 10,000 yen/W.